Process for treating skins for the manufacture of leather



Patented Oct. 22, 1940 UNITED STATES PROCESS FOR TREATING SKINSFOR THE MANUFACTURE OF LEATHER Bunyan H. Little, Wilmington, DeL, assignor to Hercules Powder Company, Wilmington, "Del., a corporation of Delaware l e No Drawing. Application Decemberl, 1938, Serial No. 243,395

'4Claims. (o 14a-c) This invention relates to the processing of leather and more particularly to that operation known as the fat-liquoring of skins.

The conversion of crude skins to finished leather consists of a series of procedures based largely on experience. Crude skins are usually received at the tannery in a dry, salted condition and .before being subjected to any treatment are swelled back into shape by, soaking in water. [Extraneous matter such as salt, tissue, dry blood, fat, hair, insoluble protein matter is then removed from these soaked hides. Ina great many instances the original skins contain variable quan titles of fatty substances such asgrease and it 15 may be desirable to remove these prior to the tanning operation because their removal permits better penetration of the tanning liquor.

Some of the natural oils are, of course, removed in the degreasing operation and this loss of oil tends to make the skins brittle and less supple than they originally were. Furthermore, even though the skins may not have been sublected to the degreasing operation prior to tanning, the tanning operation in: itself, although it lessens the tendency of the individual fibers to stick together, it doesnot lubricate them so that they will slip freely over each other and thus tends to make the leather rather hard and brittle. It has, therefore, been a practice for many years to subject the skins, after the tanning operation, to a fat-liquoring process,'in which oils and greases are incorporated into the skins to lubricate the fibers thereof and soften the skins, thus making them more pliable, increasing the strength and the resistance to tearing.

Heretofore it has been the practice to fatliquor skins by treating the skins after the. tanning operation in a rotary drum or similar appapenetrate into the skins to some extent and lubricate and soften the individual fibers. A fatliq'uor emulsion usually consists of an oil such as cod liver oil, neats-foot oil; an emulsifying agent,

such as, a sulfonated oil, soap, egg yolk, moellon degras or combinations thereof and water and sometimes a material such as borax, sodium carbonate, etc., to adjust the pH.

The chief difiiculty, however, with prior art fatu liquoring compositions has been the fact that the ratus with emulsions of oily materials which became too loose and raggy to make a satisfac-' tory andsalable product, although the leather itself was smoother, of finer grain, and of greater area yield. In order to give the finished leather the necessary tightness and stand, it was'neces- 6 sary tomake a compromise and leave the middle layer of the leather substantially un-fat-liquored; As a consequence, the middlelayer, upon drying of the skins, tended to shrink more than the'outer layer and resulted not only in a loss in area yield 10 v v v but, of greater importance, in a loss in the quality of the skin, because the grain surface tended to becomeroughened as a result of the unequal shrinkage of the layers. Various methods have been used .in the past for correcting these diflil5 culties, but none of them have satisfactorily solved the problem presented. i It is the object of my invention to provide a process whereby fat-liquoring maybe carried out in a manner so that not only the outer layers are fat-liquored, but that the whole skin is uniformly treated throughout, without, however, making the skins so treated loose and raggy and thus less salable.

The process in accordance with my invention 25 comprises adding to water-wet skins, after they have been tanned and before or after dyeing, a water emulsion of a fat-liquoring composition containing a minor amount of pine oil, agitating the skins with this combination, wither-without the addition of protective colloid to. stabilize the emulsion, and thereafter removing the skins from the treating material and subjecting the skins to various finishing operations commonly carried out in the art.

I have found that skins treated in accordance with my invention are uniformly fat-liquored throughout without, however, producing a ragginess or looseness of the skins as heretofore obtained when complete penetration of the skins 0 occurred. I attribute this to the penetrating power of the pine oil which enables me to obtain substantially complete fat-liquoring throughout the whole skin without the use of excessive amounts of the fat-liquor. Thus by mymethod of fat-liquoring, using a composition containing a minor amount of pine oil, I am enabled to make a leather which is smoother, has a finer grain,

is more supple and pliable and at the same time 7 50 has the necessary tightness, i. e., it is not loose and raggy.

In proceeding in accordance with my invention I may take water-wet skins such as cow'hides, calves skins, sheep skins and the like, after they have been tanned and either before or after dyemg, and place them in a suitable rotating drum or similar device. To these skins I may then add a water emulsion of a fat-liquoring composition containing a minor amount of pine oil and then treat the skins with this composition for about 15 minutes to 1 hour at a temperature within the range from about 100 F; to about 140 F. After this the skins may be removed and subjected to further steps in the art of leather processing, such as, glazing, etc. In the fat-liquoring step in general it is desirable to incorporate oil,-

to the extent of about 4% into the skins.

The particular fat-liquoring. composition used, in addition to the pine oil, will depend on the skins treated as well as the practice prevalent in each leather treating establishment. Various animal and vegetable oils may be used for the purpose and various agents may be used to form the emulsion. It is common practice today to use an oil such as cod liver oil or neats-foot oil or a sulfonated oil or an oxidized oil together with an emulsifying agent such as a sulfonated oil, for example, sulfonated neats-foot oil, sulfonated cod liver oil, sulfonated castor oil, etc., egg yolk, soap, etc., or various mixtures thereof. In general, it is desirableto adjust the composition of the fat-liquoring bath to such a point that prac-' tically all of the oil is used, thus allowing the spent liquor to be discarded with as little loss as possible' Generally speaking, it may be stated that the amount of the oils in-the fat-liquoring composition will vary'from about 3% to about 10% by weight of the skins on a dry basis.

The amount of pin oil used with the fat-liquoring composition, because of the widely difierent formulae used in the tanneries, will also be quite variable. I have found in general, howeveig'that a fat-liquoring composition containing from about 2% to about 15% of pine oil on the basis of the oil used in any particular fat-liquor composition is' the 'most satisfactory, and produces leather having the desirable properties before given.

In some cases, it may also be desirable to add protective colloids to act as stabilizing agents for the emulsion. As stabilizers a great varietyof mostly water-soluble colloided substances may be used among which are, for example, gum

arabic, albumin, agar agar, and methyl cellulose.

The following example will give a more detailed description of the process in accordance with my invention Example One hundred and sixty-one pounds of cow hides were placed in a rotating drum and dyed. The following fat-liquoring composition was then emulsified in 8 gallons of water and added to the hides in the drum, the dispersed phase of the emulsion so produced having the following composition:

Pounds Egg yolk 1.42 Sulfonated neats-foot oil 6.40 Fig soap 0.54 Oxidized cod liver oil 1.35 Sulionated cod liver oil 0.75 "Pine oil- 0.62

,Theskins were then tumbled with this emulsion for 40 minutes at a temperature of approximately l. The process for fat-liquoring skins whichcomprises treating skins with a water emulsion of a fat-liquoring composition containing a minor amount of pine oil.

2. A process for fat-liquoring skins which comprises treating skins with a water emulsion of a fat-liquoring composition containing pine oil in an amount within the rangefrom about 2% to about 15% on the basis of the oils present in the said fat-liquoring composition.

3. The process for fat=liquoring skins which comprises treating skins with a water emulsion of a fat-liquoring composition containing a protective colloid and pine oil in an amount within the range from about 2% to about 15% onthe basis'of the oils present in said fat-liquoring composition.

4. The process for fat-liquoring skins which comprises treating skins with a water emulsion of a fat-liquoring composition containing pine oil in an amount within the range from about 2% to about 15% on the basis of the oils present in said fat-liquoring composition, agitating the skins with said. emulsion for about 15 minutes to 

